Others have described the use of microwave energy to dry agricultural products. Use of microwave energy to cure tobacco is disclosed in U.S. Pat. No. 4,430,806 to Hopkins. In U.S. Pat. No. 4,898,189, Wochnowski teaches the use of microwaves to treat green tobacco in order to control moisture content in preparation for storage or shipping. In U.S. Pat. No. 3,699,976, microwave energy is described to kill insect infestation of tobacco. Moreover, techniques using impregnation of tobacco with inert organic liquids (U.S. Pat. No. 4,821,747) for the purposes of extracting expanded organic materials by a sluicing means have been disclosed wherein the mixture was exposed to microwave energy. In another embodiment, microwave energy is disclosed as the drying mechanism of extruded tobacco-containing material (U.S. Pat. No. 4,874,000). In U.S. Pat. No. 3,773,055, Stungis discloses the use of microwave to dry and expand cigarettes made with wet tobacco.
Prior attempts to reduce tar and harmful carcinogenic nitrosamines primarily have included the use of filters in smoking tobacco. In addition, attempts have been made to use additives to block the effects of harmful carcinogens in tobacco. These efforts have failed to reduce the oncologic morbidity associated with tobacco use. It is known that fresh-cut, green tobacco has virtually no nitrosamine carcinogens. See, e.g., Wiernik et al, "Effect of Air-Curing on the Chemical Composition of Tobacco," Recent Advances in Tobacco Science, Vol. 21, pp. 39 et seq., Symposium Proceedings 49th Meeting Tobacco Chemists' Research Conference, Sep. 24-27, 1995, Lexington, Ky. (hereinafter "Wiernik et al"). However, cured tobacco is known to contain a number of nitrosamines, including the harmful carcinogens N'-nitrosonornicotine (NNN) and 4-(N-nitrosomethylamino)-1-(3-pyridyl) -1-butanone (NNK). It is widely accepted that such nitrosamines are formed post-harvest, during the curing process, as described further herein. Unfortunately, fresh-cut green tobacco is unsuitable for smoking or other consumption.
In 1993 and 1994, Burton et al at the University of Kentucky carried out certain experiments regarding tobacco-specific nitrosamines (TSNA), as reported in the Abstract, "Reduction of Nitrite-Nitrogen and Tobacco N'-Specific Nitrosamines In Air-Cured Tobacco By Elevating Drying Temperatures", Agronomy & Phytopathology Joint Meeting, CORESTA, Oxford 1995. Burton et al reported that drying harvested tobacco leaves for 24 hours at 71.degree. C., at various stages of air curing, including end of yellowing (EOY), EOY+3, EOY+5, etc. resulted in some reduction of nitrosamine levels. Reference is also made to freeze drying and microwaving of certain samples, without detail or results. Applicant has confirmed that in the actual work underlying this Abstract, carried out by Burton et al at the University of Kentucky, the microwave work was considered unsuccessful. Certain aspects of Burton et al's 1993-94 study are reported in Wiernik et al, supra, at pages 54-57, under the heading "Modified Air-Curing". The Wiernik et al article postulates that subjecting tobacco leaf samples, taken at various stages of air-curing, to quick-drying at 70.degree. C. for 24 hours, would remove excess water and reduce the growth of microorganisms; hence, nitrite and tobacco-specific nitrosamine (TSNA) accumulation would be avoided. In Table II at page 56, Wiernik et al includes some of Burton et al's summary data on lamina and midrib nitrite and TSNA contents in the KY160 and KY171 samples. Data from the freeze-drying and the quick-drying tests are included, but there is no mention of the microwaved samples. The article contains the following conclusion:
It can be concluded from this study that it may be possible to reduce nitrite levels and accumulation of TSNA in lamina and midrib by applying heat (70.degree. C.) to dark tobacco after loss of cell integrity in the leaf. Drying the tobacco leaf quickly at this stage of curing reduces the microbial activity that occurs during slow curing at ambient temperature. It must be added, however, that such a treatment lowers the quality of the tobacco leaf. PA1 subjecting at least a portion of the plant to microwave radiation, while said portion is uncured and in a state susceptible to having the amount of nitrosamines reduced or formation of nitrosamines arrested, for a sufficient time to reduce the amount of or substantially prevent formation of at least one nitrosamine. PA1 rehydrating the cured brown tobacco, and PA1 subjecting the rehydrated tobacco to microwave radiation at a predetermined energy level for a predetermined length of time. PA1 rehydrating the cured brown tobacco, and PA1 subjecting the rehydrated tobacco to microwave radiation at a predetermined energy level for a predetermined length of time. PA1 subjecting harvested tobacco leaves to microwave radiation, while said leaves are uncured and in a state susceptible to having the amount of tobacco-specific nitrosamines reduced or formation of tobacco-specific nitrosamines arrested, for a sufficient time to reduce the amount of or substantially prevent formation of at least one tobacco-specific nitrosamine in the leaves, and PA1 forming the tobacco product comprising the microwaved leaves, the tobacco product being selected from cigarettes, cigars, chewing tobacco, snuff and tobacco-containing gum and lozenges.
Id. at page 56. The Weirnik et al article also discusses traditional curing of Skroniowski tobacco in Poland as an example of a 2-step curing procedure. The article states that the tobacco is first air-cured and, when the lamina is yellow or brownish, the tobacco is heated to 65.degree. C. for two days in order to cure the stem. An analysis of tobacco produced in this manner showed that both the nitrite and the TSNA values were low, i.e., less than 10 micrograms per gram and 0.6-2.1 micrograms per grams, respectively. Weirnik et al theorized that these results were explainable due to the rapid heating which does not allow further bacterial growth. Weirnik et al also noted, however, that low nitrite and TSNA values, less than 15 micrograms per gram of nitrite and 0.2 microgram per gram of TSNA, were obtained for tobacco subjected to air-curing in Poland.